In reply to:
chess, are you sure that the artifact is not specific to the DSP and its firmware used in your Onkyo receiver?
No sushi, i'm not sure of that at all.
I was testing the subwoofers at the time and made a mental note that i thought the surround sounds from some of the recordings was rather odd (again something not as easily noticed when the main speakers are playing the primary volumes).
I never did go back to sift through a couple of other recordings to see how the surround sound is reproduced with DPL2. It is possible that the tracks i had heard were mixed with this effect in mind (referring to the main stereo units, not specifically the surround speakers).